Moving object communication systems

ABSTRACT

Radio interference of a moving object communication system, wherein radio communication is between ground stations and a moving object such as a train, with other communication systems which is caused by the electromagnetic coupling between a leaky waveguide and an antenna aboard the moving object, is greatly reduced by providing a ground structure supporting the leaky waveguide in such a way that a narrow space or channel is left between the ground structure and the body of the moving object adjacent the direct coupling space between the line and the antenna. An electromagnetic wave absorbing substance is provided in this narrow space or channel and further the channel is preferebly additionally provided with corners in order to attenuate unwanted interference with other communication systems.

, United States Patent N akahara et a1.

[451 Apr. 25, 1972 MOVING OBJECT COMMUNICATION SYSTEMS Tsuneo Nakahara;Noritaka Kurauchi;

Hiroshi Kitani; Kenji Takemura, all of Osaka, Japan Inventors:

Sumitomo Electric Industries, Ltd., Osaka, Japan Filed: Mar. 31, 1970Appl. No.: 24,240

Assignee:

Foreign Application Priority Data Apr. 1, 1969 Japan ..44/24365 U.S. Cl...246/1 R, 246/30, 343/713, 343/717, 325/51, 325/52 Int. Cl. ..H0lq 1/32Field of Search ..246/8, 30; 343/18A,71 1,712, 343/713, 717; 325/51, 52

References Cited UNITED STATES PATENTS Hafner..... ..246/8 x Pickles..343/18 A X Primary EraminerArthur L. La Point Assistant ExaminerGeorgeH. Libman Attorney-Carothers and Carothers 5 7] ABSTRACT Radiointerference of a moving object communication system, wherein radiocommunication is between ground stations and a moving object such as atrain, with other communication systems which is caused by theelectromagnetic coupling between a leaky waveguide and an antenna aboardthe moving object, is greatly reduced by providing a ground structuresupporting the leaky waveguide in such a way that a narrow space orchannel is left between the ground structure and the body of the movingobject adjacent the direct coupling space between the line and theantenna. An electromagnetic wave absorbing substance is provided in thisnarrow space or channel and further the channel is prefereblyadditionally provided 7 Claims, 11 Drawing Figures BACKGROUND OF THEINVENTION 1. Field of the Invention This invention relates to acommunication system for moving objects such as trains.

2. Description of the Prior Art I-Ieretofore, in a train or movingobject communication system, radio communication between ground stationsand trains was done such that an electromagnetic wave of uniformintensity was radiated from a leaky wave guide connected to the groundstations along the rail road track and which was coupled with an antennaaboard a train. With such an arragement, however, unexpectedinterference waves from other commercial communication systems oftenintrude, while on the other hand waves from such a system interfere withother communication system because of their leaking from the place ofcoupling between the leaky wave guide and the antenna aboard the train.

Generally speaking, the interference noise level at the receiver onboard the moving vehicle and which is connected to the train antenna, isvery high or serious, while the interference noise level at the receiverlocated at the ground stations and connected to the leaky waveguide isnot serious. The electromagnetic waves from other communication systemcouple strongly to the train antenna, while they couple weakly to theleaky waveguide because they greatly attenuate when they enter awaveguide.

SUMMARY OF. THE INVENTION The present invention has as a principleobject, the reduction of interference between other communicationsystems and the train communication system, particularly such othersystems found at a train station. In order to attain this object, thepresent invention uses a device which reduces the radiation power ofelectromagnetic waves eminating from the train antenna without affectingthe degree of coupling between the train antenna and the leakywaveguide. As means to carry this out, two embodiment may be used inaccordance with the teachings of the present invention.

The first means is performed by the absorption of electromagnetic waveswhich would radiate outwards in undesired directions from the trainantenna by means of a wave absorbing substance disposed around the trainantenna.

The second means is performed by the absorption of electromagnetic wavesby way of attenuation due to diffraction of electromagnetic waves at acorner of a narrow space between a train body and a ground structure.

BRIEF EXPLANATION OF THE DRAWING FIG. 1 is a diagrammatic sectional viewshowing the rela tionship between an antenna on a train and a leakywaveguide for the communication system of the present invention.

FIG. 2 is a diagrammatic perspective view of the measurement device forthe explanation of the principle of the present invention.

FIG. 3 is a diagrammatic front elevation of the same device shown inFIG. 2, and

FIG. 4 and FIG. 5 are characteristics graphs showing the results ofmeasurements made from the afore-said measurement device.

FIG. 6 and FIG. 7 are diagrammatic sectional views in elevation showingother example embodiments.

FIG. 8 is also a diagrammatic perspective view of a measurement devicefor the explanation of the principles of the present invention.

FIG. 9 is a characteristics graph showing the measurement results.

FIG. 10 and FIG. 11 are diagrammatic sectional views in front elevationshowing other examples of embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an exampleembodiment of this invention according to the first aforementionedmeans.

In FIG. I, 1 denotes the leaky waveguide, 3 the main body of the train,5 the electromagnetic wave absorbing substance disposed around theantenna, 6 the duct for the installation of the waveguide alongthe-indicated tracks, and 7 a ground structure on the railroad trackwhich supports the leaky waveguide and which is installed near to thetrain, for the object of this invention, to prevent the leakage ofelectromagnetic waves. The ground structure is made of such a materialas metal, concrete, etc. which reflects electromagnetic waves or whichabsorbs electromagnetic waves to some degree, though not completely.2cand 2d denote parts constituting the train antenna, 2Q being a'primaryradiator of the traveling wave type made of a rectangular waveguide, and2d being a secondary radiator made of a metal reflector having anelliptical cylinder shape. D is a narrow spacing between the train body3 and the ground structure 7.

The principle of the first example means of the present invention isthat the electromagnetic wave radiated by the train antenna istransmitted well to the leaky waveguide in the duct 6, but that portionwhich is apt to pass through the narrow channel region defining space Dbetween the ground structure 7 and the electromagnetic wave absorbingsubstance 5 disposed around the antenna on the train body as shown bythe arrows of the broken lines, is subjected to great attenuation. Thus,the amount of electromagnetic wave radiation directed outwards becomesvery small.

It should be noted that the width of the narrow channel region, asdefined by the width of the electromagnetic wave absorbing substance 5,is significant, meaning that it is of sufficient width such that thewave absorbing material can effectively attenuate the electromagneticwaves passing through the channel region.

Now a model experimental apparatus for confirming this attenuation ofthe outwardly directed electromagnetic waves will be explained. FIG. 2is a perspective view of the experimenting apparatus. FIG. 3 is itsfront elevation. Rectangular waveguides 13, 14 are placed between planesof metal 11 and 12, the appertures of the waveguides being opposed atthe distance Z to each other. The distance between 11 and 12 isrepresented by d. The rectangular waveguide 13 is connected to anoscillator and the rectangular waveguide 14 to a receiver. The distancebetween their appertures is represented by Z.

With the above-described apparatus, the rectangular waveguide 13 on thetransmission side is fixed and the rectangular waveguide 14 on thereceiver side is moved forward and back to vary the distance Z betweenthe appertures of the two waveguides, and the changes in the amount ofattenuation of electromagnetic waves with respect to distance 2 aremeasured.

FIG. 4 shows the results of the above-mentioned measurements. In thatfigure, the abscissa is the distance 2, expressed in mm, between theappertures of the transmitting and receiving rectangular waveguides,while the ordinate is attenuation between the transmitting and receivingwaveguide. The curvea represents the results when metal was used forboth 11 and 12 of FIG. 2 and FIG. 3, while the curve-b represents theresults when metal was used for 11 and an electromagnetic wave absorbingsubstance was used in place of metal for 12,

with the frequency at the time of measurement being 10 6H,,

and the distance between metals l1 and 12, d 20 mm.

From these measurement results, it is obviously noted that theattenuation with the curve-b, using an electromagnetic wave absorbingsubstance on one side, is much greater than that with the curve-a usingmetal on both sides, and that an electromagnetic wave is subject togreat attenuation when passing through a space between a metal plate andelectromagnetic wave absorbing substance.

FIG. shows the results of measurement of the variations in theattenuation of an electromagnetic wave versus the distance d between themetal plate 11 and the electric wave absorbing substance 12, whilekeeping a constant distance 2 between the appertures of theaforementioned rectangular waveguides 13 and 14. The ratio of thedistance d to the wavelength A, d/)., is shown on the abscissa and theratio of the attenuation, Art, to the wavelength A, Art/k, is shown onthe ordinate.

According to FIGS. 4 and 5, it is noted that when the distance d betweenthe metal plate and the electromagnetic wave absorbing substance is muchshorter than the wavelength, the attenuation is great, so that it ishighly effective. Attenuation of 2.7 db per wavelength is obtained whend M5. To the contrary, as d becomes much longer than the wavelength,attenuation per wavelength decreases. When a' 3)., the attenuation is0.5 db per wavelength and when d d 6A, it is 0.1 db.

If the traveling length of the electromagnetic wave in the gap between(11) and (12) is assumed to be 1,000 mm and A 30 mm, A then= 3 db whend=6A andA= 15 db whend= 3). Technically, it is desirable that there bean attenuation of more than db. For this reason, a distance d of 4 orless is suitable.

As described above, electromagnetic waves can be attenuated effectivelyby making the distance small between the electromagnetic wave absorbingsubstance and the metal body.

What has been mentioned above refers to the utilization of theattenuation of electromagnetic waves by reducing the distance betweenthe electromagnetic wave absorbing substance and the metal object to 4Aor less. If the electromagnetic wave absorbing substance is used inplace of the other metal body also, the effective utilization of theattenuation of electromagnetic waves can be made until the distancebetween the electromagnetic wave absorbing substance and the otherelectromagnetic wave absorbing substance reaches two times 4A, i.e. 8).,because of the principle of mirror image. Thereflection coefficient ofconcrete is l3 db. This is larger than the reflection coefficient 26 dbof an ordinary electromagnetic wave absorbing substance. In this case,however, a similar effect was obtained where the distance was 6A orless. Now a substance such as concrete, which is somewhat less effectivein the absorption of electromagnetic waves,'is called asemi-electromagnetic wave absorbing substance, and the metal plate iscalled wave reflecting substance.

FIG. 6 shows an example embodiment wherein the system of the presentinvention based, on the above-described measurement results, is madeapplicable to an air or magnetic suspension train which is expected tobe developed in the future.

In FIG. 6, 1 denotes a leaky waveguide, 2a and 2b the primary andsecondary radiators of the train antenna respectively, 3 the main bodyof the train, 5 and electromagnetic wave absorbing substance, 6 a ductto house the leaky waveguide, and 8 the road floor made of concrete orthe like. In this case, the spacing between the train and the road floorwill be made very small, so that the train antenna and theelectromagnetic wave absorbing substance can be brought very near to theroad floor. Electromagnetic waves radiated from the train antenna to theoutside through space D attenuate very greatly.

The second means of the present invention consists in the utilization ofattenuation due to diffraction of electric waves, at a corner of thenarrow space between train body and a ground structure or floor. Anembodiment of the present invention according to the second means isshown in FIG. 7.

In case the device according to the present invention is used, theelectromagnetic waves radiated from the train antennas 2a and 2b coupledirectly with the waveguide l and at the same time part of them areradiatedoutward through the space between the road floor 8 and theelectromagnetic wave absorbing substance 5. Unlike the aforementionedspace, this space is provided with a corner P, and the present inventiontakes advantage of the attenuation which occurs when electromagneticwaves diffract at this corner. The results of experimental measurementof the attenuation of electromagnetic waves at such a corner are shownhereinafter.

FIG. 8 shows an apparatus for this experiment. 1 l is a metal body, 12an electromagnetic wave absorbing substance, 13 a rectangular waveguideon the transmission side, and 14 a rectangular waveguide on thereceiving side, the appertures of these waveguide being spaced at thedistance Z. Point P is, as in FIG. 7, the corner of the electromagneticwave passage of an electromagnetic wave absorbing substance. While anelectromagnetic wave comes out from the rectangular waveguide 13 on thetransmission side, passes the part P and reaches the rectangularwaveguide 14 on the receiving side, it undergoes great attenuation.

The results of measurement by the above-mentioned experiment are shownin FIG. 9. In that figure, the abscissa represents the distance Zbetween the appertures of the waveguides on the transmission and thereceiving side, expressed in millimeters. The ordinate represents thedegree of attenuation, Art of, electromagnetic waves, expressed indecibels. The curve-a and curve-b of FIG. 4 are transcribed on FIG. 9for reference, the curve-a showing attenuation for waves passing betweentwo metal bodies and the curve-b showing the attenucation of wavespassing between a metal body and an electromagnetic wave absorbingsubstance. The curve-c shows the results of measurement made by theaforementioned apparatus shown in FIG. 8. The part-Q of the curve-cshows the attenuation due to the bend of the electromagnetic wavepassage, i.e. part-P as shown in the FIG. 8. The attenuation due to thecorner, namely the difference between the curve-b and the curve-c at thepart-Q, amounts to approximately 20 db for the wave of a wavelength of30 mm. This remarkable amount of attenuation is very suitable for thepurpose of the present invention. According to the results ofexperiment, theamount of attenuation due to the corner is very muchgreater than that due to the reduction of the distance d between themetal body and the electromagnetic wave absorbing substance.

As mentioned above, increasing the attenuation of electromagnetic wavesis efi'ected by providing a corner in a space between the train body andthe ground structure as shown in FIG. 7. In addition to the attenuationcreated by a corner. great attenuation will alsobe obtained, as alreadystated, in a rectilinear passage,if the space is made small.

FIG. 10 and FIG. 11 show other examples of embodiment of the presentinvention. In both examples of the two figures, corner portionschanneling electromagnetic waves are provided in the space between theelectromagnetic wave absorbing substance 5 and the road floor 8.

In these examples, one corner is provided in the space to either side ofthe antenna. However such a corner shall not be limited to one, but thegreater the number of such corners provided in the space between thetrain and ground structure is, the more effective it will be to increaseattenuation.

The first and the second means of this invention have been described indetail. If this invention is used, electromagnetic waves emitting from atrain antenna are prevented from useless radiation from the traincommunication system by installing an electromagnetic wave absorbingsubstance in the neighborhood of the antenna aboard the train, thuseliminating interference between the train communication systems andother communication system.

In the aforementioned examples of the embodiment, electromagnetic waveabsorbing substance is placed only in the neighborhood of the antennaaboard the train. However, it should not necessarily be installed on thetrain. It goes without saying that the same effect can be obtained alsoby installing such a substance in the neighborhood of the waveguide onthe ground or in the neighborhood of both.

Throughout the foregoing description, a leaky waveguide has always beenused for the transmission line on the ground vfor train communication.However, the present invention is not to be limited to systems where aleaky waveguide is used. It is equally applicable to systems using aleaky coaxial cable, which is a coaxial cable provided with leakyapperture, or a surface wave line, or the like. Such lines shalltherefore be given a generic name hereinafter as an open typetransmission line.

What we claim is:

1. A communication coupling system for a moving vehicle following apredetermined path, comprising a support structure following said pathand supporting a continuous opentype transmission line therealong spacedadjacent to an antenna mounted on a vehicle on said path for movementthereover and continuously providing an electromagnetic coupling spacebetween said line and said antenna while said vehicle is in motion, saidsupport means providing a continuous reflective or semi-electromagneticwave absorbing surface behind said transmission line opposite to saidcoupling space, the surfaces of said support structure and said vehicledefining a closely spaced channel region therebetween of significantwidth and at least coextensive with said antenna on at least one side ofsaid electromagnetic coupling space, at least one of the surfaces insaid channel region including electromagnetic wave absorbing material toattenuate electromagnetic waves passing through said channel region.

2. The communication coupling system of claim 1 wherein said channelregion spacing is maintained to be no greater than approximately eightwavelengths of the electromagnetic wave in use for coupling between saidline and said antenna.

3. The communication coupling system of claim 2 characterized in thatsaid. closely spaced channel region passes through at least one comer.

4. The communication system of claim 2 wherein both of the opposedsurfaces of said channel include electromagnetic wave absorbingproperties.

5. The communication coupling system of claim 2 wherein said channelregion extends from both sides of said coupling region between saidsupportstructure and said vehicle to attenuate all electromagnetic wavesescaping from said coupling space.

6. The communication system of claim 2 wherein said wave absorbing meansis capable of attenuation of said electromagnetic waves passing throughsaid channel region of more than 10 db.

7. The communication system of claim 1 wherein only one of said channelsurfaces has electromagnetic wave absorbing properties and the spacingbetween said surfaces of said channel region is maintained at no morethan four wavelengths of the wavelength in use.

1. A communication coupling system for a moving vehicle following apredetermined path, comprising a support structure following said pathand supporting a continuous open-type transmission line therealongspaced adjacent to an antenna mounted on a vehicle on said path formovement thereover and continuously providing an electromagneticcoupling space between said line and said antenna while said vehicle isin motion, said support means providing a continuous reflective orsemielectromagnetic wave absorbing surface behind said transmission lineopposite to said coupling space, the surfaces of said support structureand said vehicle defining a closely spaced channel region therebetweenof significant width and at least coextensive with said antenna on atleast one side of said electromagnetic coupling space, at least one ofthe surfaces in said channel region including electromagnetic waveabsorbing material to attenuate electromagnetic waves passing throughsaid channel region.
 2. The communication coupling system of claim 1wherein said channel region spacing is maintained to be no greater thanapproximately eight wavelengths of the electromagnetic wave in use forcoupling between said line and said antenna.
 3. The communicationcoupling system of claim 2 characterized in that said closely spacedchannel region passes through at least one corner.
 4. The communicationsystem of claim 2 wherein both of the opposed surfaces of said channelinclude electromagnetic wave absorbing properties.
 5. The communicationcoupling system of claim 2 wherein said channel region extends from bothsides of said coupling region between said support structure and saidvehicle to attenuate all electromagnetic waves escaping from saidcoupling space.
 6. The communication system of claim 2 wherein said waveabsorbing means is capable of attenuation of said electromagnetic wavespassing through said channel region of more than 10 Db.
 7. Thecommunication system of claim 1 wherein only one of said channelsurfaces has electromagnetic wave absorbing properties and the spacingbetween said surfaces of said channel region is maintained at no morethan four wavelengths of the wavelength in use.